1. Field of the Invention
This invention pertains generally to concrete slipform sleds, and more particularly to a sled for extruding curbs and gutters.
2. Description of Related Art
Curbs and gutters in new streets are typically formed by extruding a flowable paving material, such as concrete, through a slipform mold which conforms to the profile of the desired curb and gutter. Typically, the standard curb has an elevated rectangular profile adjacent to the gutter, which has a lower, relatively flat profile. A self propelled paving machine is typically used to extrude a continuous curb and gutter. A slipform sled having a hopper and the slipform is attached to the paving machine and positioned for a continuous pour. Flowable paving material is placed in the hopper of the sled and flows into the mold by gravity where it is extruded out behind the sled while the sled moves forward. Vibrators are typically placed in the hopper to help move the paving material into the mold, remove voids and produce a uniform surface on the extruded curb and gutter.
A driveway curb profile is typically lower than the standard curb. In some existing slipform sleds, when a driveway section needs to be made, a knife plate is inserted into the curb section mold to scrape the concrete extrusion to the driveway curb level. This knife plate causes the concrete extruded below it to come out with a ragged surface and little or no elevation control. The scraped driveway curb must be hand finished by first installing a form to the backside to establish the driveway curb elevation. The driveway curb is then floated to the form elevation, radius edges are installed and the curb surface smoothed with a trowel Taper forms are used to finish the transition from standard curb to driveway curb.
In another configuration of existing curb and gutter paving systems, a tail piece is lowered behind the slip mold to cut or squeeze the curb extrusion to a lower elevation. In other systems a plate within the slip mold is lowered in elevation for a driveway curb. These methods depend on the travel of a hydraulic cylinder actuator pressing against extruded paving material to be uniform for each change of elevation. Unfortunately, these systems do not exhibit consistent uniform elevation control. They typically result in wasted concrete and usually leave a rough, uneven curb surface that requires form leveling and significant hand finishing. In still further systems, the sled must stop and the slipform mold exchanged to the desired curb profile for each driveway transition.
In a new home development, dozens of driveway sections may be installed in the curbs and gutters paved in a single day. With existing equipment, this requires many starts and stops to exchange molds or significant labor to set forms and hand finish the driveway curb elevations.
What is needed is a slipform sled that can extrude both the standard elevation curb and a lower elevation driveway curb reliably and without requiring significant finishing by hand.